We study the extent to which us urban development is sprawling and what determines differences in sprawl across space. Using remote-sensing data to track the evolution of land use on a grid of 8.7 billion 30×30 meter cells, we measure sprawl as the amount of undeveloped land surrounding an average urban dwelling. The extent of sprawl remained roughly unchanged between 1976 and 1992, although it varied dramatically across metropolitan areas. Ground water availability, temperate climate, rugged terrain, decentralized employment, early public transport infrastructure, uncertainty about metropolitan growth, and unincorporated land in the urban fringe all increase sprawl.Key words: urban sprawl, land development, remote sensing jel classification: r14, o51 * For helpful comments and suggestions we thank three anonymous referees, William Fischel, Masahisa Fujita, John Hartwick, Vernon Henderson, John Landis, William Strange, and, in particular, Edward Glaeser. We also received helpful comments from seminar participants at the University of California Berkeley, Harvard University, Universitat Pompeu Fabra and Stanford University, and at conferences organized by the Regional Science Association International, the Centre for Economic Policy Research, the Association of Environmental and Resource Economists, and the Lincoln Institute. We are very grateful to Ferko Csillag for his advice on remote-sensing data. Also to the us Geological Survey, and in particular to Stephen Howard and James Vogelmann, for early access to preliminary versions of the 1992 data. Vernon Henderson and Jordan Rappaport kindly provided us with data on metropolitan population 1920-1990, Matthew Kahn with data on employment decentralization, and Jacob Vigdor with data on streetcar usage. While working on this project, Burchfield was an MSc student at the Department of Geography, University of Toronto. She gratefully acknowledges help from Kent Todd in preparing arc Macro Language scripts. Funding from the Social Sciences and Humanities Research Council of Canada (Puga and Turner), and the support of the Canadian Institute for Advanced Research (Puga) and the National Fellows program at the Hoover Institution (Turner) are gratefully acknowledged.† Neptis Foundation, 50 Park Road, Toronto, Ontario m4w 2n5, Canada (e-mail: mburchfield@neptis.org). ‡ Department of Geography and Environment, London School of Economics, Houghton Street, London wc2a 2ae, United Kingdom (e-mail: h.g.overman@lse.ac.uk; website: http://cep.lse.ac.uk/~overman). Also affiliated with the Centre for Economic Policy Research, and the Centre for Economic Performance at the London School of Economics.§ Department of Economics, University of Toronto, 150 Saint George Street, Toronto, Ontario m5s 3g7, Canada (e-mail:d.puga@utoronto.ca; website: http://dpuga.economics.utoronto.ca). Also affiliated with the Canadian Institute for Advanced Research and the Centre for Economic Policy Research. ¶ Department of Economics, University of Toronto, 150 Saint George Street, Toronto, On...